Ho-hum. Audi won the 12-hour Sebring endurance race again in 2006, making it seven in a row. What's different about the latest victory is the car's powerplant: a diesel engine. This is the first time a diesel-engine vehicle has triumphed in a major automobile endurance race. And it's also a shot in the arm for the image of diesels, which account for nearly half of all passenger cars sold in Europe but for only a fraction in the U.S.

The LeMans Prototype Audi R10, with its V12 turbocharged diesel engine producing 650 hp, finished four laps ahead of the runner-up. A sister R10 diesel retired at the midpoint while leading; Audi called the retirement "precautionary." (Translation: An overheating problem from track debris clogging the radiator fins could have caused embarrassing engine failure.) From Sebring, it's on to the most famous of all endurance races—the 24-hours LeMans, in June.

Audi had a slight advantage going into the race: Rules allow slightly bigger diesel engines than gasoline engines, with more turbocharger boost (pressure), and a gallon of diesel fuel has 12 percent more energy than gasoline. Other diesel-engine cars have competed in major races, but have had less success. A Cummins diesel racer won the starting pole position for the 1952 Indianapolis 500, but wound up finishing 27th.